Communications emails not sending

The communications are not sending, for neither the triggers or the 'send to me' test. I have looked around the forums and it looks like Cron gets a big mention but most topics were solved by a past update.

Looking at the database it appears messages are being sent as the usermeta values for sent_msgs_1 is populated for the users. (currently set to trigger on registration) but nothing is ever delivered.

Other auto delivery messages are working like new user notifications and have tried setting up smtp to see if it made any difference. It sounds like it is something to do with the cron but I would have though the 'send to me' test should still work?

Any help very much appreciated.

Kind Regards

James